|Power at 4500m||900hp|
|Wing area (biplane)||20.83m2|
|Wing area (monoplane)||13.0m2|
|Weights and loads|
|Wing load (takeoff)||111|
|Wing load (cruise)||177|
|Power load (kg/hp)||2.56|
|4*7.62mm ShKAS (1000 rounds)|
The 'IS' series stands for Istrebitel Skladnoj (Folding Fighter) - unique compromise between biplane and monoplane fighters: it was both. The lower wing could be retracted upwards, flush with the forward fuselage and the upper wing, while the wheels retracted into the lower wing surfaces.
This concept may be considered one of the first (and successful!) to implement variable geometry wing. 'IS' in its biplane configuration had excellent takeoff/landing characteristics and increased payload, while switching to monoplane scheme in flight allowed reach higher speed and range.
V.V.Nikitin started working on the plane in 1938, but real boost to the project came from pilot/engineer V.V.Shevchenko. As a result, new design bureau was organized in 1939 - OKB-30. V.V.Shevchenko became Designer General, and V.V.Nikitin - his first deputy.
Fuselage for new aircraft was borrowed from the N.N.Polikarpov I-153 fighter. Upper wing was replaced by one with larger span but narrower chord. Lower wing had two folding points: one at the root and another at about mid-span on each side. Hydraulic jacks with indigenous system of levers provided perfectly synchronous operation on both sides. 'Hamilton' 3-blade propeller (d=2.8m) was fitted.
IS-1 was completed in late 1939 and flown soon after by LII test-pilot G.M.Shijanov (factory trials). The first in-flight translation from monoplane to biplane and back again was in June of 1940, proving that the concept was workable. Nonetheless, IS-1 was found inferior against conventional monoplane fighters (MiG-3, LaGG-2, Yak-1) and was not permitted to State Trials.
But the concept was not yet completely abandoned.
|46k drawing by I.G.Soultanov from "History of aircraft construction in the USSR", Vol.2 p.101, used as a background for this page;|